Devices, systems, and methods for sychronizing a remote receiver to a master signal for measuring scattering parameters

ABSTRACT

A reflectometer for use in measuring scattering (S-) parameters for a device under test (DUT) includes a test port, a radio frequency (RF) output signal source, and a local oscillator (LO) signal. The LO signal is used to downconvert the RF output signal to an incident IF signal. The reflectometer is useable as a master reflectometer with a slave reflectometer such that the master reflectometer provides the slave reflectometer with a synchronization signal to synchronize signals generated by the second reflectometer to the incident IF signal. Phase and magnitude of transmission S-parameters of the DUT are measurable when the reflectometer is used as the master reflectometer in combination with the slave reflectometer. The master reflectometer and the slave reflectometer can be reconfigurable to reverse the master/server roles of the reflectometers.

TECHNICAL FIELD

The present invention relates to devices and method for synchronizing aremote receiver to a master signal for measuring scattering parameters.

BACKGROUND

Scattering (S-) parameters (the elements of a scattering matrix)describe the electrical behavior of linear electrical networks anddevices when undergoing various steady state stimuli by electricalsignals. The parameters are useful for electrical engineering,electronics engineering, and communication systems design, includingmicrowave engineering. Many electrical properties of networks ofcomponents (inductors, capacitors, resistors) may be expressed usingS-parameters, including gain, return loss, voltage standing wave ratio(VSWR), reflection coefficient and amplifier stability. Althoughapplicable at any frequency, S-parameters are mostly used for networksoperating at radio frequency (RF) and microwave frequencies where signalpower and energy considerations are more easily quantified than currentsand voltages. S-parameters change with the measurement frequency, sofrequency must be specified for any S-parameter measurements stated, inaddition to the characteristic impedance or system impedance.

Vector network analyzers can be used to measure S-parameters, and varyin the number of ports usable to connect with a network or device. Thenetwork or device itself can have multiple ports. Vector networkanalyzers designed for simultaneously measuring the S-parameters ofnetworks or devices with more than two ports are feasible but quicklybecome prohibitively complex and expensive. Commonly, a single portmeasurement of the input port voltage reflection coefficient is useful.Combining two single port vector reflectometers can provide flexibilityand potentially reduce costs where single port measurements are morecommonly obtained, but where multi-port measurements can be beneficialas well.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a single port reflectometer in accordance with the prior art.

FIG. 1B is a circuit diagram of a system in accordance with the priorart for measuring two port scattering parameters for a device undertest.

FIG. 2 is a circuit diagram of an embodiment of a system in accordancewith the present invention for measuring two port scattering parametersfor a device under test.

FIG. 3 is a circuit diagram of an alternative embodiment of a system inaccordance with the present invention for measuring two port scatteringparameters for a device under test.

FIG. 4 is a circuit diagram of an alternative embodiment of a system inaccordance with the present invention for measuring two port scatteringparameters for a device under test.

FIG. 5 is a circuit diagram of an alternative embodiment of a system inaccordance with the present invention for measuring two port scatteringparameters for a device under test.

FIG. 6 is a circuit diagram of an alternative embodiment of a system inaccordance with the present invention for measuring two port scatteringparameters for a device under test.

FIG. 7 is a circuit diagram of an alternative embodiment of a system inaccordance with the present invention for measuring two port scatteringparameters for a device under test.

FIG. 8 is a simplified circuit diagram of an alternative embodiment of asystem in accordance with the present invention for measuring two portscattering parameters for a device under test.

FIG. 9 is a flow diagram of a method for measuring scattering parametersin accordance with the present invention.

DETAILED DESCRIPTION

The following description is of the best modes presently contemplatedfor practicing various embodiments of the present invention. Thedescription is not to be taken in a limiting sense but is made merelyfor the purpose of describing the general principles of the invention.The scope of the invention should be ascertained with reference to theclaims. In the description of the invention that follows, like numeralsor reference designators will be used to refer to like parts or elementsthroughout. In addition, the first digit of a reference numberidentifies the drawing in which the reference number first appears.

It would be apparent to one of skill in the art that the presentinvention, as described below, may be implemented in many differentembodiments of hardware, software, firmware, and/or the entitiesillustrated in the figures. Further, the frequencies given for signalsgenerated and/or used in the figures and description are merelyexemplary. Any actual software, firmware and/or hardware describedherein, as well as any frequencies of signals generated thereby, is notlimiting of the present invention. Thus, the operation and behavior ofthe present invention will be described with the understanding thatmodifications and variations of the embodiments are possible, given thelevel of detail presented herein.

FIG. 1A illustrates a single port reflectometer 100 in accordance withthe prior art for use in measuring electrical performance of adevice-under-test (DUT). The reflectometer 100 is connectable with asecond reflectometer, for example via a ⅛″ diameter, 6′ cable with microcoaxial (MCX) connectors (not shown), and controllable via a universalserial bus (USB) cable (Control I/O). FIG. 1B is a circuit diagram of asystem including the single port reflectometer 100 in accordance withthe prior art for measuring the electrical behavior of a device ornetwork when the device or network is connected with a test port P1 as aDUT. The single port reflectometer 100 includes a time base signalsource 102 generating a time base signal that synchronizes a pair ofoscillators via respective phase-locked loops (PLLs) 104, 114 togenerate a radio frequency (RF) output signal that is transmitted to thetest port P1 and a local oscillator (LO) signal that is used todownconvert the RF output signal via a first mixer 118 to generate anincident intermediate frequency (IF) signal. As shown, the time basesignal has a frequency of 26 MHz, the RF output signal has a frequencyof 4.6 MHz, and the LO signal has a frequency of 4.7 MHz.Synchronization using the time base signal allows the mixer 118 togenerate a resulting incident IF signal having a reliable frequency of100 KHz.

A reflected signal generated at the DUT and reflected back to the testport P1 is coupled to a second mixer 108 and the LO signal is used todownconvert the reflected signal to generate a reflected IF signal. Asynchronous detector (not shown) uses the incident and reflected IFsignals to measure a scattering (S-) parameter of the DUT. The singleport reflectometer 100, when used alone, can measure an S-parametercorresponding to the input port voltage reflection coefficient (alsoreferred to as the S11 parameter). The single port reflectometer 100 canmeasure magnitude and phase of the input port reflection coefficient.

As further shown in FIG. 1B, the prior art single port reflectometer 100can be used as a master reflectometer with a second single portreflectometer 150 acting as a slave reflectometer, with both the masterand slave reflectometers being connected with a DUT at the respectivetest ports P1, P2 of the reflectometers. The slave reflectometer 150receives the time base signal generated by the master reflectometer 100via a second cable to synchronize the time base frequencies of the tworeflectometers 100, 150. The time base synchronization can avoidvariation in frequency between different crystal oscillators within thereflectometers which can result, for example, in differences of hundredsof hertz. The time base signal received from the master reflectometer100 synchronizes a local oscillator via a PLL 164 to generate an LOsignal.

The RF source of the slave reflectometer 150 is switched off and anincident IF signal of the slave reflectometer 150 is disabled. The slavereflectometer 150 receives at the second test port P2 the RF outputsignal transmitted from the first test port P1 to the DUT. The RF outputsignal is coupled to and downconverted by a mixer 158 using thesynchronized LO signal, allowing the measurement of magnitude for anadditional S-parameter for the DUT corresponding to the forward voltagegain (i.e., the magnitude portion of the S21 parameter).

Additionally, with the RF source of the master reflectometer 100switched off and the RF source of the slave reflectometer 150 switchedon, the time base signal received from the master reflectometer 100synchronizes an oscillator via a PLL 154 to generate the RF outputsignal that is transmitted to the test port P2. The slave reflectometer150 can be used to measure the phase and magnitude of the reversereflection coefficient (i.e., the S22 parameter). Further, the masterreflectometer 100 can receive at the first test port P1 an RF outputsignal transmitted from the second test port P2 to the DUT allowing themeasurement of magnitude for a third S-parameter corresponding to thereverse voltage gain (i.e., the magnitude portion of the S12 parameter).

Phase information can be obtained for the S11 parameter because the sameLO signal is used to downconvert RF signals to generate the incident andreflected IF signals when measuring the S11 parameter. However, themaster and slave reflectometer 100, 150 arrangement of FIG. 1B onlyallows measurement of magnitude for the S21 and S12 parameters. The LOsources of the two reflectometers 100, 150 generate LO signals havingpredictable frequencies due to the common time base signal, but thephases of the two LO signals are not synchronized, are indeterminable,and can vary because they are generated using different dividers 116,166, with each divider 116, 166 comprising separate divide-by-twocounters. A counter can come up in either state (0 or 1) when turned on.The more signal division, the more ambiguity in the phase state of theLO signal. As a result, phase information for the S21 and S12 parameterscannot be obtained via the arrangement of FIG. 1.

Embodiments of devices, systems, and methods in accordance with thepresent invention can be used to synchronize a remote receiver to amaster signal for measuring both phase and magnitude for two portS-parameters obtained via the remote receiver. Such embodiments can beused to measure both phase and magnitude of the S11 and S22 parametersfor a DUT as described above with respect to FIG. 1B. However they alsoallow the measurement of phase and magnitude for additionalS-parameters, rather than measurement of magnitude alone.

FIG. 2 is circuit diagram of an embodiment of a system for measuringS-parameters in accordance with the present invention comprising a firstsingle port reflectometer 200 usable as a master reflectometer and asecond single port reflectometer 250 usable as a slave reflectometer. AnRF source of each of the reflectometers is switchably connectable to anddisconnectable from a port P1, P2 so that either reflectometer can actas a transmitter while the other reflectometer acts as a receiver. Asshown, the master reflectometer 200 is switched to transmit an RF outputsignal to a DUT (not shown) connected between the test ports P1, P2,while the slave reflectometer 250 is switched to receive the transmittedsignal.

The master reflectometer 200 includes a time base signal source 202 thatprovides a time base signal usable by both the master reflectometer 200and the slave reflectometer 250 to synchronize the signals generated bythe reflectometers. The time base signal can be passed from the masterreflectometer 200 to the slave reflectometer 250 via a cable, forexample a coaxial cable having micro coaxial (MCX) connectors. As shown,the time base signal has a frequency of 100 KHz.

When the master reflectometer 200 is switched to act as a transmitter,the time base signal acts as a synchronization (SYNC) signal to a pairof dividers 216, 206 to synchronize an LO signal generated from a clock(CLK) signal provided by a first PLL 214 to an RF output signalgenerated from a CLK signal provided by a second PLL 204. The RF outputsignal is downconverted by the synchronized LO signal at a mixer (asshown) 218 to generate an incident IF signal having a predictable phaseas well as frequency. As shown, the RF output signal has a frequency of4.6 MHz, and the LO signal has a frequency of 4.7 MHz. The resultingincident IF signal has a frequency of 100 KHz. Matching the time basesignal frequency to the incident IF signal frequency can simplify thecircuit diagram, although in other embodiments, the frequencies of thetime base signal and incident IF signal need not be matched.

The time base signal further acts as a SYNC signal to a divider 266 ofthe slave reflectometer 250 to synchronize the LO signal generated froma CLK signal provided by a PLL 264 to the incident IF signal generatedby the master reflectometer 200. The RF output signal transmitted by themaster reflectometer 200 to the DUT and received at the test port P2 iscoupled to a mixer 258 and downconverted by the synchronized LO signalto generate a transmitted IF signal having a phase synchronized with theincident IF signal, enabling the measurement of both magnitude and phaseof the S21 parameter.

When the slave reflectometer 250 is switched to act as a transmitter andthe master reflectometer 200 is switched to act as a receiver, the timebase signal of the master reflectometer acts as a SYNC signal to thepair of dividers 256, 266 of the slave reflectometer 250 to synchronizean LO signal generated from a CLK signal provided by the first PLL 264to an RF output signal generated from a CLK signal provided by a secondPLL 254. The RF output signal is downconverted by the synchronized LOsignal at a mixer 258 to generate an incident IF signal having apredictable phase as well as frequency. The time base signal furtheracts as a SYNC signal to a divider 216 of the master reflectometer 200to synchronize the LO signal generated from a CLK signal provided by aPLL 214 to the incident IF signal generated by the slave reflectometer250. The RF output signal transmitted by the slave reflectometer 250 tothe DUT and received at the test port P1 is coupled to a mixer 208 anddownconverted by the synchronized LO signal to generate a transmitted IFsignal synchronized with the incident IF signal, enabling themeasurement of both magnitude and phase of the S12 parameter.

FIG. 3 is a circuit diagram of an alternative embodiment of a system formeasuring S-parameters in accordance with the present inventioncomprising a first single port reflectometer 300 usable as a masterreflectometer and a second single port reflectometer 350 usable as aslave reflectometer. As with the previous embodiment, an RF source ofeach of the reflectometers 300, 350 is switchably connectable to anddisconnectable from a port P1, P2 so that either reflectometer can actas a transmitter while the other reflectometer acts as a receiver. Asshown, the master reflectometer 300 is switched to transmit an RF outputsignal to a DUT (not shown) connected between the test ports P1, P2while the slave reflectometer 302 is switched to receive the transmittedsignal.

The master reflectometer 300 includes a time base signal source 302 thatprovides a time base signal to synchronize a CLK signal provided by aPLL 304 and a SYNC signal generated by dividing the CLK signal using aCLK divider 310. The SYNC signal is usable by the master reflectometer300 to synchronize the phase of signals generated by the masterreflectometer. The SYNC signal can be passed from the masterreflectometer 200 to the slave reflectometer 250 via a cable. As shown,the time base signal and SYNC signal each have a frequency of 100 KHz.

When the master reflectometer 300 is switched to act as a transmitter,the SYNC signal is provided to a pair of dividers 306, 316 tosynchronize an LO signal and an RF output signal, both generated fromthe CLK signal. The RF output signal is downconverted by the LO signalat a mixer 318 to generate an incident IF signal. The RF output signalhas a frequency of 4.6 MHz, and the LO signal has a frequency of 4.7MHz. The resulting incident IF signal has a frequency of 100 KHz. TheSYNC signal is passed to the slave reflectometer 350 and usable by theslave reflectometer 350 to synchronize a CLK signal provided by a PLL354 and a second SYNC signal generated by dividing the CLK signal usinga CLK divider 360. The second SYNC signal is provided to a divider 366of the slave reflectometer 350 to synchronize the LO signal generatedfrom the CLK signal to the incident IF signal of the masterreflectometer 300. The RF output signal transmitted by the masterreflectometer 300 to the DUT and received at the test port P2 of theslave reflectometer 350 is coupled to a mixer 358 and downconverted bythe synchronized LO signal at the mixer 358 to generate a transmitted IFsignal synchronized with the incident IF signal, enabling themeasurement of both magnitude and phase of the S21 parameter.

When the slave reflectometer 350 is switched to act as a transmitter andthe master reflectometer 300 is switched to act as a receiver, the SYNCsignal synchronized with the time base signal of the masterreflectometer 300 synchronizes a CLK signal provided by a PLL 354 and asecond SYNC signal generated by dividing the CLK signal using a CLKdivider 360. The second SYNC signal is provided to a pair of dividers356, 366 of the slave reflectometer 350 to synchronize an LO signal toan RF output signal, both generated from the CLK signal provided by thefirst PLL 354. The RF output signal is downconverted by the synchronizedLO signal at a mixer 258 to generate an incident IF signal having apredictable phase as well as frequency. The SYNC signal synchronized bythe time base signal is provided to a divider 316 of the masterreflectometer 300 to synchronize the LO signal generated from the CLKsignal provided by the PLL 304 to the incident IF signal of the slavereflectometer 350. The RF output signal transmitted by the slavereflectometer 350 to the DUT and received at the test port P1 of themaster reflectometer 300 is downconverted by the synchronized LO signalat a mixer 308 to generate a transmitted IF signal having a predictablephase, enabling the measurement of both magnitude and phase of the S12parameter.

FIG. 4 is a circuit diagram of an alternative embodiment of a system formeasuring S-parameters in accordance with the present inventioncomprising a first single port reflectometer 400 usable as a masterreflectometer and a second single port reflectometer 450 usable as aslave reflectometer. As shown, the master reflectometer 400 is switchedto transmit an RF output signal to a DUT (not shown) connected betweenthe test ports P1, P2 while the slave reflectometer 450 is switched toreceive the transmitted signal.

The master reflectometer 400 includes a time base signal source 402 thatprovides a time base signal to synchronize signals generated by themaster reflectometer 400. With the master reflectometer 400 switched toact as a transmitter, the time base signal acts as a SYNC signal to apair of dividers 416, 406 to synchronize an LO signal generated from aCLK signal provided by a first PLL 414 to an RF output signal generatedfrom a CLK signal provided by a second PLL 404. As shown, the PLLoscillator and divider need not be identical between the LO and RFsources. The RF output signal is downconverted by the synchronized LOsignal at a mixer 418 to generate an incident IF signal having apredictable phase as well as frequency. As shown, the time base signalhas a frequency of 100 KHz, the RF output signal has a frequency of 4.6MHz, and the LO signal has a frequency of 4.7 MHz. The resultingincident IF signal has a frequency of 100 KHz.

The incident IF signal of the master reflectometer 400 provides areference (REF) signal to the slave reflectometer 450 to synchronize thesignals generated by the reflectometers 400, 450. The amplitude of atransmitted signal can vary for environmental and performance reasons.For example, reflectometers require a warm up period until performancereaches a generally steady state. Warm up periods of 30 minutes arecommon in commercially available reflectometers. The REF signal variesin amplitude with the transmitted signal so that variation in thetransmitted signal can be accounted for when measuring S-parameters.

The REF signal is provided to a divider 466 of the slave reflectometer450 to synchronize the LO signal generated from a CLK signal provided bya PLL 464 to the incident IF signal of the master reflectometer 400. TheRF output signal transmitted by the master reflectometer 400 andreceived by the slave reflectometer 450 at the test port P2 is coupledto a mixer 458 and downconverted by the synchronized LO signal at themixer 458 to generate a transmitted IF signal synchronized with theincident IF signal, enabling the measurement of both magnitude and phaseof the S21 parameter. Because the incident IF signal of the masterreflectometer 400 is used as the REF signal, the RF source of the masterreflectometer 400 must be switched to act as a transmitter when usedwith a slave reflectometer 450 to obtain two port measurements.

FIG. 5 is a circuit diagram for an alternative embodiment of a systemfor measuring S-parameters in accordance with the present inventioncomprising a first single port reflectometer 500 usable as a masterreflectometer and a second single port reflectometer 550 usable as aslave reflectometer. As shown, the master reflectometer 500 is switchedto transmit an RF output signal to a DUT connected between the testports P1, P2 while the slave reflectometer 550 is switched to receivethe transmitted signal.

The master reflectometer 500 includes a time base signal source 502 thatprovides a time base signal to synchronize a CLK signal provided by aPLL 504 and a SYNC signal generated by dividing the CLK signal using aCLK divider 510. The SYNC signal is usable by the master reflectometer500 to synchronize the signals generated by the master reflectometer500. As shown, the time base signal and SYNC signal each have afrequency of 100 KHz.

The SYNC signal of the master reflectometer 500 is provided to a pair ofdividers 516, 506 to synchronize an LO signal and an RF output signal,both generated from the CLK signal provided by the PLL 504. The RFoutput signal is downconverted by the synchronized LO signal at a mixer518 to generate an incident IF signal having a predictable phase as wellas frequency. As shown, the RF output signal has a frequency of 4.6 MHz,and the LO signal has a frequency of 4.7 MHz. The resulting incident IFsignal has a frequency of 100 KHz. The incident IF signal of the masterreflectometer 500 provides a REF signal to the slave reflectometer 550to synchronize the signals generated by the reflectometers 500, 550. Aswith the previous embodiment, the REF signal varies in amplitude andfrequency with the transmitted signal so that variation in thetransmitted signal can be removed when measuring S-parameters.

The REF signal is provided to a PLL 554 of the slave reflectometer 550to synchronize a CLK signal generated by the PLL 554 and a second SYNCsignal generated by dividing the CLK signal using a CLK divider 560. TheLO signal is generated from the CLK signal by the divider 566 andsynchronized to the incident IF signal of the master reflectometer 500by the second SYNC signal. The RF output signal transmitted by themaster reflectometer 500 and received by the slave reflectometer 550 atthe test port P2 is coupled to a mixer 558 and downconverted by thesynchronized LO signal at the mixer 558 to generate a transmitted IFsignal synchronized with the incident IF signal, enabling themeasurement of both magnitude and phase of the S21 parameter. Becausethe incident IF signal of the master reflectometer 500 is used as theREF signal, the RF source of the master reflectometer 500 must beswitched to act as a transmitter when used with a slave reflectometer550 to obtain two port measurements.

FIG. 6 is circuit diagram of an alternative embodiment of a system formeasuring S-parameters in accordance with the present invention. Thesystem comprises a first single port reflectometer 600 usable as amaster reflectometer and a second single port reflectometer 650 usableas a slave reflectometer. The reflectometers each use a high frequencytime base signal source 602, 652, such as used by the masterreflectometer in FIG. 1B. As shown, the master reflectometer 600 isswitched to transmit an RF output signal to a DUT connected between thetest ports P1, P2 while the slave reflectometer 650 is switched toreceive the transmitted signal.

The master reflectometer 600 includes a time base signal source 602 thatprovides a time base signal that is used to synchronize CLK signalsprovided by a pair of PLLs 604, 614 and a SYNC signal generated bydividing the time base signal using a base divider 610. The SYNC signalis usable by the master reflectometer 600 to synchronize the signalsgenerated by the master reflectometer 600. As shown, the time basesignal has a frequency of 26 MHz and the SYNC signal has a frequency of100 KHz.

The SYNC signal is provided to a pair of dividers 616, 606 tosynchronize an LO signal generated from a CLK signal provided by thefirst PLL 614 to an RF output signal generated from a CLK signalprovided by the second PLL 604. The RF output signal is downconverted bythe synchronized LO signal at a mixer 618 to generate the incident IFsignal having a predictable phase as well as frequency. As shown, the RFoutput signal has a frequency of 4.6 MHz, and the LO signal has afrequency of 4.7 MHz. The resulting incident IF signal has a frequencyof 100 KHz, and provides a REF signal to the slave reflectometer 650 tosynchronize the signals generated by the reflectometers 600, 650. Aswith the previous embodiment, the REF signal varies in amplitude andfrequency with the transmitted signal so that variation in thetransmitted signal can be removed when measuring S-parameters.

Unlike previous embodiments, a time base signal source 652 of the slavereflectometer 650 is used for generating signals. The time base signalsource 652 provides a time base signal that is used to synchronize a CLKsignals provided by a pair PLL 654, 664 and a second SYNC signalgenerated by dividing the time base signal using a base divider 660. TheREF signal synchronizes the divider 660 of the time base signal to theincident IF signal of the master reflectometer 600. The second SYNCsignal is provided to a divider 667 to synchronize an LO signalgenerated from a CLK signal provided by the first PLL 664 to theincident IF signal of the master reflectometer 600. The RF output signaltransmitted by the master reflectometer 600 and received by the slavereflectometer 650 at the test port P2 is coupled to a mixer 658 anddownconverted by the synchronized LO signal at the mixer 658 to generatea transmitted IF signal synchronized with the incident IF signal,enabling the measurement of both magnitude and phase of the S21parameter. Because the incident IF signal of the master reflectometer600 is used as the REF signal, the RF source of the master reflectometer600 must be switched to act as a transmitter when used with a slavereflectometer 650 to obtain two port measurements.

FIG. 7 is circuit diagram of an alternative embodiment of a system formeasuring S-parameters in accordance with the present invention. Thesystem comprises a first single port reflectometer 700 usable as amaster reflectometer and a second single port reflectometer 750 usableas a slave reflectometer. The master reflectometer includes a highfrequency time base signal source 702, such as used by the masterreflectometer in FIG. 1B. As shown, the master reflectometer 700 isswitched to transmit an RF output signal to a DUT connected between thetest ports P1, P2 while the slave reflectometer 650 is switched toreceive the transmitted signal.

The system resembles the system of FIG. 6, but uses frequency diplexers712, 762 connected, for example via a cable, to provide both a time basesignal to synchronize PLLs 704, 714, 754, 764 of the both the masterreflectometer 700 and the slave reflectometer 750 and a REF signalprovided to the signal dividers 756, 766 of the slave reflectometer. Theuse of frequency diplexers eliminates the time needed for locking aseparate time base signal source for the slave reflectometer 750,thereby substantially reducing the point by point measurement time.

The master reflectometer 700 provides the time base signal that is usedto synchronize CLK signals provided by a pair of PLLs 704, 714 and aSYNC signal generated by dividing the time base signal using a basedivider 710. The SYNC signal is usable by the master reflectometer 700to synchronize the signals generated by the master reflectometer 700. Asshown, the time base signal has a frequency of 26 MHz and the SYNCsignal has a frequency of 100 KHz.

The SYNC signal is provided to dividers of the PLLs and a pair ofdividers 716, 706 to synchronize an LO signal generated from a CLKsignal provided by the first PLL 714 to an RF output signal generatedfrom a CLK signal provided by the second PLL 704. The RF output signalis downconverted by the synchronized LO signal at a mixer 718 togenerate the incident IF signal having a predictable phase as well asfrequency. As shown, the RF output signal has a frequency of 4.6 MHz,and the LO signal has a frequency of 4.7 MHz. The resulting incident IFsignal has a frequency of 100 KHz and provides a REF signal for theslave reflectometer 750 to synchronize the signals generated by thereflectometers 700, 750. As with the previous embodiment, the REF signalvaries in amplitude and frequency with the transmitted signal so thatvariation in the transmitted signal can be removed when measuringtransmission S-parameters S21 and S12.

The time base signal of the master reflectometer 700 is passed to theslave reflectometer 750 to synchronize a PLL 764 of the slavereflectometer 700 to the time base signal. The REF signal is provided todividers of the PLL 764 and a divider 766 that generates the LO signalfrom a CLK signal provided by the first PLL 764 to synchronize the LOsignal to the incident IF signal of the master reflectometer 600. The RFoutput signal transmitted by the master reflectometer 600 and receivedby the slave reflectometer 750 at the test port P2 is coupled to a mixer658 and downconverted by the synchronized LO signal at the mixer 758 togenerate a transmitted IF signal synchronized with the incident IFsignal, enabling the measurement of both magnitude and phase of the S21parameter. Because the incident IF signal of the master reflectometer700 is used as the REF signal, the RF source of the master reflectometer700 must be switched to act as a transmitter when used in with a slavereflectometer 700 to obtain two port measurements.

FIG. 8 is a simplified circuit diagram of an alternative embodiment of asystem for measuring S-parameters in accordance with the presentinvention allowing two reflectometers to be interchangeably used asmaster and slave reflectometers. The embodiment can allow the sale, forexample, of a single stock keeping unit (SKU) for a particular solution.The embodiment can also reduce mismatching of devices at test sites, forexample, and allows a purchaser to divide the single port reflectometersup for some tests while combining them for others.

The system comprises a first single port reflectometer 800 configured asa master reflectometer (switch configuration “M”) and a second singleport reflectometer 850 configured as a slave reflectometer (switchconfiguration “S”). The RF source 806, 856 and LO source 816, 866 aregeneralized relative to previous embodiments, as different componentscan be used to obtain the signals needed to generate a target frequencyfor an incident IF signal. As shown, the master reflectometer 800 isswitched to transmit an RF output signal to a DUT connected between thetest ports P1, P2 while the slave reflectometer 850 is switched toreceive the transmitted signal.

When the master reflectometer 800 is switched to act as a transmitter, atime base source 802 of the master reflectometer 800 generates a timebase signal to synchronize an LO signal generated by the LO source 816to an RF output signal generated by the RF source 806. The time basesignal provides a CLK signal to the RF and LO sources, as well as a SYNCsignal generated by a master sync divider (MSD) 820. The RF outputsignal transmitted by the master reflectometer 800 is downconverted bythe synchronized LO signal at a mixer 818 to generate an incident IFsignal (a1) having a predictable phase as well as frequency. The timebase signal is passed to the slave reflectometer 850 via connectedfrequency diplexers 812,862 to provide a clock signal to the LO source866 of the slave reflectometer 850. The incident IF signal generated bythe master reflectometer 850 is used as a REF signal and passed to theslave reflectometer 850 via the frequency diplexers 812, 862 tosynchronize the LO source 856 to the incident IF signal. The RF outputsignal transmitted by the master reflectometer 800 to the DUT andreceived at the test port P2 of the slave reflectometer 850 is coupledto a mixer 818 and downconverted by the synchronized LO signal at themixer 858 to generate a transmitted IF signal (b2) synchronized with theincident IF signal, enabling the measurement of both magnitude and phaseof the S21 parameter (S21=b2/a1).

When the slave reflectometer 850 is switched to act as a transmitter, atime base source 852 of the slave reflectometer 850 generates a timebase signal to synchronize an LO signal generated by the LO source 866to an RF output signal generated by the RF source 856. The RF outputsignal transmitted by the slave reflectometer 850 is downconverted bythe synchronized LO signal at a mixer 868 to generate an incident IFsignal (a2) having a predictable phase as well as frequency. The timebase signal is passed to the slave reflectometer 850 via connectedfrequency diplexers 812,862 to provide a clock signal to the LO source816 of the master reflectometer. The incident IF signal (a2) generatedby the slave reflectometer 850 is used as a REF signal and passed to themaster reflectometer 800 via the frequency diplexers 812, 862 tosynchronize the LO source 806 to the incident IF signal. The RF outputsignal transmitted by the slave reflectometer 850 to the DUT andreceived at the test port P1 of the master reflectometer 800 is coupledto a mixer 808 and downconverted by the synchronized LO signal at themixer 808 to generate a transmitted IF signal (b1) synchronized with theincident IF signal (a2), enabling the measurement of both magnitude andphase of the S12 parameter (S12=b1/a2).

FIG. 9 is a flowchart of a method for measuring S-parameter inaccordance with the present invention. The method comprises using afirst single port reflectometer configured as a master reflectometer(Step 900) and using a second single port reflectometer configured as aslave reflectometer (Step 902). The DUT is connected to the single portof the master reflectometer and the single port of the slavereflectometer (Step 904). The master reflectometer is configured togenerate an RF output signal and an LO signal to downconvert the RFoutput signal to an incident IF signal. The master reflectometerprovides a base signal to the slave reflectometer to generate an LOsignal to downconvert the RF output signal transmitted by the masterreflectometer to the DUT to a transmit IF signal. The masterreflectometer further provides a synchronization signal to the slavereflectometer to synchronize the transmit IF signal with theintermediate IF signal. The forward magnitude and phase for scatteringparameters S11 and S21 of the DUT can be measured based on the incidentIF signal and the transmit IF signal (Step 906).

The method can further comprise reconfiguring the first single portreflectometer and the second single port reflectometer. The reversemagnitude and phase for scattering parameters S22 and S12 of the DUT canbe measured based on a second incident IF signal from the reconfiguredsecond single port reflectometer and a transmit IF signal from thereconfigured first single port reflectometer. Reconfiguring can compriseswitching the RF source of the second single port reflectometer ON andthe RF source of the first single port reflectometer OFF. Reconfiguringcan also comprise reconfiguring the first single port reflectometer asthe slave reflectometer and the second single port reflectometer as themaster reflectometer.

The present invention may be conveniently implemented using one or moreconventional general purpose or specialized digital computer, computingdevice, machine, or microprocessor, including one or more processors,memory and/or computer readable storage media programmed according tothe teachings of the present disclosure. Appropriate software coding canreadily be prepared by skilled programmers based on the teachings of thepresent disclosure, as will be apparent to those skilled in the softwareart.

In some embodiments, the present invention includes a computer programproduct which is a storage medium or computer readable medium (media)having instructions stored thereon/in which can be used to program acomputer to perform any of the processes of the present invention. Thestorage medium can include, but is not limited to, any type of diskincluding floppy disks, optical discs, DVD, CD-ROMs, microdrive, andmagneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, DRAMs, VRAMs, flashmemory devices, magnetic or optical cards, nanosystems (includingmolecular memory ICs), or any type of media or device suitable forstoring instructions and/or data.

The previous description of the preferred embodiments is provided toenable any person skilled in the art to make or use the embodiments ofthe present invention. While the invention has been particularly shownand described with reference to preferred embodiments thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the invention.

The invention claimed is:
 1. A reflectometer for use in measuringscattering (S-) parameters for a device under test (DUT), comprising: atest port configured to receive signals and selectively transmitsignals; a first signal source selectively connectable with the testport and configured to provide a radio frequency (RF) output signal tothe test port; and a second signal source configured to provide a localoscillator (LO) signal to downconvert one or both of a received signalto a reflected intermediate frequency (IF) signal and the RF outputsignal to an incident IF signal; wherein when the reflectometer is usedas a master reflectometer with a slave reflectometer, the reflectometerprovides the slave reflectometer with a synchronization signal to phasesynchronize signals generated by the slave reflectometer to the incidentIF signal; and wherein both phase and magnitude of an S21 parameter ofthe DUT are measurable at the reflectometer when the reflectometer isused as the master reflectometer in combination with the slavereflectometer.
 2. The reflectometer of claim 1, wherein when thereflectometer is used as a slave reflectometer in combination with amaster reflectometer, the reflectometer receives from the masterreflectometer a synchronization signal to phase synchronize signalsgenerated by the reflectometer to an incident IF signal of the masterreflectometer; and wherein both phase and magnitude of an S12 parameterof the DUT are measurable at the reflectometer when the reflectometer isused as the slave reflectometer in combination with the masterreflectometer.
 3. The reflectometer of claim 1, further comprising: abase signal source configured to provide a base signal; wherein the RFoutput signal provided by the first signal source and the LO signalprovided by the second signal source are synchronized using the basesignal.
 4. The reflectometer of claim 3, wherein the synchronizationsignal is obtained from the base signal.
 5. The reflectometer of claim1, wherein the synchronization signal is phase synchronized with theincident IF signal and has an amplitude varying with the incident IFsignal, and wherein the synchronization signal is obtained from theincident IF signal.
 6. The reflectometer of claim 1, wherein the firstsignal source includes a first fractional divider that receives a clocksignal from a phase locked loop (PLL) connected with the base signalsource and a sync signal from the base signal source to generate the RFoutput signal such that the RF output signal is phase synchronized withthe base signal; and wherein the second signal source includes a secondfractional divider that receives the clock signal from the PLL and thesync signal from the base signal source to generate the LO signal suchthat the LO signal is phase synchronized with the base signal.
 7. Thereflectometer of claim 1, wherein the first signal source includes afirst fractional divider that receives a first clock signal from a firstphase locked loop (PLL) connected with the base signal source and afirst sync signal from the base signal source to generate the RF outputsignal such that the RF output signal is phase synchronized with thebase signal; and wherein the second signal source includes a secondfractional divider that receives a second clock signal from a second PLLconnected with the base signal source and a second sync signal from thebase signal source to generate the LO signal such that the LO signal isphase synchronized with the base signal.
 8. The reflectometer of claim3, further comprising: a diplexer for providing both the synchronizationsignal and the base signal to the slave reflectometer.
 9. A system formeasuring scattering (S-) parameters for a device under test (DUT),comprising: a first reflectometer including a test port configured toreceive signals and selectively transmit signals, a first signal sourceselectively connectable with the test port and configured to provide aradio frequency (RF) output signal to the test port, and a second signalsource configured to provide a local oscillator (LO) signal todownconvert one or both of a received signal to a received intermediatefrequency (IF) signal and the RF output signal to an incident IF signal;a second reflectometer including a test port configured to receivesignals and selectively transmit signals, a first signal sourceselectively connectable with the test port and configured to provide anRF output signal to the test port, and a second signal source configuredto provide an LO signal to downconvert one or both of a received signalto a received IF signal and the RF output signal to an incident IFsignal; wherein the first reflectometer is configurable as a masterreflectometer with the second reflectometer configurable as a slavereflectometer such that the first reflectometer provides the secondreflectometer with a synchronization signal to phase synchronize signalsgenerated by the second reflectometer to the incident IF signal of thefirst reflectometer; wherein when the first reflectometer is configuredas the master reflectometer, the received IF signal of the firstreflectometer is a reflected IF signal and the received IF signal of thesecond reflectometer is a transmit IF signal generated from the RFoutput signal of the first reflectometer; and wherein both phase andmagnitude of an S21 parameter of the DUT are measurable at the firstreflectometer when the first reflectometer is configured as the masterreflectometer in combination with the second reflectometer configured asthe slave reflectometer.
 10. The system of claim 9, wherein the secondreflectometer is configurable as a master reflectometer with the firstreflectometer configurable as a slave reflectometer such that the secondreflectometer provides the first reflectometer with a synchronizationsignal to phase synchronize signals generated by the first reflectometerto the incident IF signal of the second reflectometer; wherein when thesecond reflectometer is configured as the master reflectometer, thereceived IF signal of the second reflectometer is a reflected IF signaland the received IF signal of the first reflectometer is a transmit IFsignal generated from the RF output signal of the second reflectometer;and wherein both phase and magnitude of an S12 parameter of the DUT aremeasurable at the first reflectometer when the second reflectometer isconfigured as the master reflectometer in combination with the firstreflectometer configured as the slave reflectometer.
 11. The system ofclaim 9, wherein the first reflectometer includes a base signal sourceconfigured to provide a base signal; wherein the RF output signalprovided by the first signal source and the LO signal provided by thesecond signal source are synchronized using the base signal.
 12. Thesystem of claim 11, wherein the synchronization signal is obtained fromthe base signal.
 13. The system of claim 9, wherein the synchronizationsignal is phase synchronized with the incident IF signal of the masterreflectometer and has an amplitude varying with the incident IF signalof the master reflectometer, and wherein the synchronization signal isobtained from the incident IF signal of the master reflectometer. 14.The system of claim 13, wherein the first reflectometer is configurableas a master reflectometer with the second reflectometer configurable asa slave reflectometer such that the master reflectometer provides theslave reflectometer with a base signal to provide a clock signal to thesecond signal source to generate the LO signal.
 15. The system of claim14, further comprising: a diplexer for providing both thesynchronization signal and the base signal to the slave reflectometer.16. The system of claim 14, wherein the first reflectometer isconfigurable as a master reflectometer with the second reflectometerconfigurable as a slave reflectometer the first signal source of themaster reflectometer includes a first fractional divider that receives aclock signal from a phase locked loop (PLL) connected with the basesignal source and a sync signal from the base signal source to generatethe RF output signal such that the RF output signal is phasesynchronized with the base signal; the second signal source of themaster reflectometer includes a second fractional divider that receivesthe clock signal from the PLL and the sync signal from the base signalsource to generate the LO signal such that the LO signal is phasesynchronized with the base signal; and wherein the second signal sourceof the slave reflectometer includes a fractional divider that receives aclock signal from the PLL generated using the base signal provided bythe master reflectometer and the synchronization signal to generate theLO signal such that the LO signal is synchronized with the incident IFsignal.
 17. A method for measuring magnitude and phase for scatteringparameters for a device-under-test (DUT), comprising: using a firstsingle port reflectometer configured as a master reflectometer; using asecond single port reflectometer configured as a slave reflectometer;connecting the DUT to the single port of the master reflectometer;connecting the DUT to the single port of the slave reflectometer;wherein the master reflectometer is configured to generate a radiofrequency (RF) output signal and a local oscillator (LO) signal todownconvert the RF output signal to an incident intermediate frequency(IF) signal; wherein the master reflectometer provides a base signal tothe slave reflectometer to generate an LO signal to downconvert the RFoutput signal transmitted by the master reflectometer to the DUT to atransmit IF signal; wherein the master reflectometer further provides asynchronization signal to the slave reflectometer to synchronize thetransmit IF signal with the intermediate IF signal; and measuringmagnitude and phase for a scattering parameter of the DUT based on theincident IF signal and the transmit IF signal.
 18. The method of claim17, further comprising: reconfiguring the first single portreflectometer as the slave reflectometer; reconfiguring the secondsingle port reflectometer as the master reflectometer; measuringmagnitude and phase for a second scattering parameter of the DUT basedon a second incident IF signal from the reconfigured second single portreflectometer and a transmit IF signal from the reconfigured firstsingle port reflectometer.